Return-spring system in a pressure-fluid cylinder



June 19, 1962 J. L. GRATZMULLER 3,039,758

RETURN-SPRING SYSTEM IN A PRESSURE-FLUID CYLINDER Original Filed July 29, 1955 n l "l INVENTOR 4W www BY )39mm r demo( ATTORNEYS United States Patent Utilice 3,li39,758 Patented June 19, 1962 3,039,758 RETURN-SPRING SYSTEM IN A PRESSURE-FLUID CYLINDER Jean Louis Gratzmuller, Avenue Georges Mandel, Paris, France Original application July 29, 1953, Ser. No. 371,007,

now Patent No. 2,796,856, dated June 25, 1957. Divided and this application June 19, 1957, Ser. No. 666,687

2 Claims. (Cl. 267-1) This invention relates to a system of coil springs to be associated, for instance, with the movable member of a pressure-fluid cylinder, suoh as the hydraulic cylinder used for actuating the rack of an automatically releasable coupling of the type described in my prior application filed July 29, 1953, under Serial No. 371,007, now Patent No. 2,796,856, issued I une 25, 1957, of which the present application is a division. Such a system has for its purpose to return said movable member into its resting position by exerting at every instant a given force thereon. In other words, the stroke and the eciency of the return system as well-defined.

In most applications, and more particularly in the abovesaid one, it is extremely desirable to reduce to a minimum the axial size of the return-spring means without, however, jeopardizing their efficiency nor increasing their diameter.

For this purpose, it has been proposed heretofore, to use several co-axial coil springs instead of a single one.

In these known systems, the springs are mounted either in parallel or in series. In the rst case, it is possible to obtain :but a slight reduction of the axial size.

When the springs are mounted in series, each one of them has to transmit, at every instant, the whole returning force. To ensure this transmission with a suitable eciency, each spring then should have a ratio between its winding diameter and the size of the wire itis made of, comprised within certain limits. Now, it happens that when a spring is mounted inside another one, which condition is indispendable in order to have them operating in series while reducing their overall length, the above-mentioned ratio can be respected with regard to one spring only.

The object of the invention is to provide a return-spring system of the type and for the purpose described, comprising three co-axial coil springs, two of which operate in parallel and are lodged within the third one which works in series with them.

This arrangement permits of reducing the axial size of the system without increasing its diameter. Furthermore, it is thus possible to give to the three springs a suitable winding diameter to wire-size ratio, while the two smaller springs, working in parallel, may be given an overall maximum power exactly equal to that of the third bigger spring.

It is another object of the invention to dispose the springs of the system in such a relative arrangement that, at the end of the active stroke of the pressure cylinder movable member, all springs are fully compressed. This last arrangement permits of still further reducing the overall axial size of the spring system.

Yet a further object of the invention is to abut the bigger outer spring against the bottom of the cylinder and the other two springs against the movable member.

If the said movable member has its end associated with the inner springs of a size slightly smaller than the inner diameter of the smaller one of said inner springs, then the said movable member end can occupy, at the end of the active stroke, the space that becomes free inside the outermost spring, when both inner ones are fully compressed (this difference of llength between the two inner springs and the outer one being due to the difference of thickness between the spring wires). This arrangement permits of reducing the overall axial size of the whole structure.

Still another object of the invention is to provide either the pressure-duid cylinder or its movable member with a guiding element lodged inside the innermost spring. This feature avoids any unsuitable lateral deformation of the two inner springs when fully extended.

Other objects and advantages of the invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example.

In these drawings:

FIGURES 1 to 3 are axial sectional views showing various known modifications of a conventional return-spring system used for returning the piston of a starter hydraulic cylinder into resting position.

FIGURE 4 is an axial sectional view of a return-spring system according to the invention, for the same use, the parts being shown in their resting position.

FIGURE 5 is a view corresponding to FIGURE 4 but showing the various parts at the end of the active stroke of the pressure-Huid cylinder piston, and

FIGURE 6 is a sectional view along line 6 6 of FIG- URE 5 In the example shown, the return-spring system according to the invention is used for returning a rack 1, meshing with the pinion 2 of a hydraulic starter coupling and constituting the piston of a hydraulic cylinder 3, in its resting position. In this example, this cylinder-rack-andpinion assembly is used for actuating the driving member of a starter coupling of the type described in the abovecited co-pending application.

FIGURE 1 shows a conventional return-spring system comprising only one spring 4 having its axis aligned with that of the cylinder 3, said spring being housed between the bottom of a tubular casing 5 and the end 6 of the rack 1 through a washer 7. The axial size of such a device, in a specic case which has been chosen as an illustration, reaches 216 mim. (about 83/'s).

In FIGURIFl 2 is shown a iirst known improvement in which three co-axial springs 8, 9 and 1t) are substituted or the single spring 4 of FIGURE l. This three-spring arrangement permits of reducing the axial size of the system in the sarne specific example only to 184.5 mm. (about 74/10), other things being equal.

In FIGURE 3 is shown another improvement comprising three co-axial return-springs in which said springs, instead of working in parallel as in FIGURE 2, are mounted in series for this purpose, a first spring 11 is interposed between the washer 7 and an outer tlange provided at one end of a movable tubular member 12; a second spring 13 -disposed inside spring 11 is interposed between an inner flange provided at the other end of said movable tubular member 12 and an outer ilange of a second movable tubular member 14; nally, a third spring 15 is interposed between an inner ange of the last-mentioned movable tubular member 14 and the bottom of the xed tubular casing 5. This arrangement permits of reducing the axial size of the return system in the same specic case to 182 mm. (about 7%0).

With this arrangement, it is impossible to obtain a suitable ratio between the Winding diameter and t'ne wire size for all three springs 11, `13 and 15. As a matter of fact, such a suitable ratio can be obtained for only one of them.

Now, it has been found that if, while using three springs, the same as adapted to work neither wholly in series nor wholly in parallel but according to a special series-parallel arrangement, the whole assembly can be made considerably more compact.

Such an arrangement is illustrated in FIGURE 4 in .E which the return spring system comprises a first spring 16 having a comparatively large cross-section which is combined with two other co-axial springs 17 and 1S of lower cross-section, so that these latter two springs work in parallel while this spring pair works in series with the spring 16. Y

This arrangement permits a greater reduction of the axial size which is decreased, again in the same specific case, to 173.6 mm. (about 7").

Furthermore, it is possible to give to the three springs 16, 17 and 18 a suitable winding diameter-to-wire size ratio while the two inner springs 17 and 18 can be given an overall maximum power substantially equal to that of the outer spring 16.

FIGURES 4 to 6 illustrate a preferred embodiment of this arrangement in which the axial size is still further reduced. In this embodiment, the diameter of the outer spring 16 is big enough for the end of rack 1 to penetrate into it. The system further comprises a freely slidable tubular member 19 between which and the cylindrical wall of the casing 5, Iis an annular space accommodating the spring 16 one end of which bears directly on the bottom of the tubular casing 5. The other end of the spring 16 bears on an outer flange 20 of the tubular member 19. The two other springs 17 and 1S are interposed between the bottom 21 of the tubular member 19 and the end of the rack 1. In the example shown, the said end carries a washer 7 which acts as an abutment for the springs 17 and 18, and a-guiding member 23 extending axially inside said springs along a length substantially equal to the distance by which they project out of the tubular member 19 in the fully-extended position shown in FIGURE 4. Moreover, in this example, the length of the tubular member 19 is equal to that of the spring 16, when the latter is fully compressed.

In the position shown in FIGURE 5, the end 6 of the rack 1 has penetrated into the movable tubular member 19, so that when the three springs are fully compressed, the axial size of the return-spring system is effectively reduced to the axial length of the spring pair 17-18. If `this preferred arrangement is compared with the other systems `described it is found that, again all other things being equal, the axial size is reduced to 156 mm. (about 61/s). Furthermore, in two comparable cases, the additional length introduced by the elastic system is, in the example of FIGURES 4 to 6, only 36 mm. instead of 96 in the example of FIGURE 1. A reduction of 63% is thus obtained. rIlhe arrangement illustrated in FIG- URES 4 to 6 further enables the whole assembly (see FIGURE 4) to have a symmetrical aspect in which the two mutually aligned tubular casings extending on either side of the casing 2'5 of the pinion 2, and respectively housing the fluid-pressure cylinder and the return-spring system, have substantially the same length.

What is claimed is:

1. An elastic return system mounted in a casing and compressible by an axially reciprocable element, said system comprising, a iirst compression coil spring bearing at one end on an end wall of said casing, a free tubular member having outer axial abutment means at one end and inner axial abutment means at its other end with an outer diameter of its cylindrical wall but slightly smaller than the inner diameter of said first spring, said tubular member being housed in said lirst spring with the other end of the latter bearing on said outer abutment means, and two other compression coil springs co-axial with said first one,

housed one inside the other within the said tubular member and interposed between said inner axial abutment means and said reciprocable element, the ratio between the winding diameter of each one of said springs and the size of the wire it is made of being comprised between such limits that the eiciency of each spring is optimum and that the maximum power of said first spring is substantially equal to the overall power of said two other springs, and sai-d tubular member having a length substantially equal to the length value of said rst spring, when the same is -iully compressed, that end of said reciprocable element which is associated with said two other springs having a diameter smaller than the inner diameter of said free tubular member at least along a distance equal to the diierence of length between said rst spring and said two other springs when all are fully compressed, and said free tubular member having a length greater than the length of said two other springs when the latter are fully compressed.

2. An elastic return system mounted in a casing and compressible by an axialy reciprocable element, said system comprising, a rst compression coil spring bearing at one end on an end wall of said casing, a free tubular member having outer axial abutment means at one end and inner axial abutment means at its other end with an outer diameter of its cylindrical wall but slightly smaller than the inner diameter of said iirst spring, said tubular member being housed in said first spring with the other end of the latter bearing on said outer abutment means, and two other compression ycoil springs co-axial with said iirst one, housed one inside the other within the said tubular member and interposed between said inner axial abutment means and said reciprocable element, the ratio between the winding diameter of each one of said springs and the size of the wire it is made of being comprised between such limits that the eiiiciency of each spring is optimum and that the maximum power of said first spring is substantially equal to the overall power of said two other springs, and said tubular member having a length substantially equal to the length value of said rst spring, when the same is fully compressed, said reciprocable element carrying an axially extending guiding member lodged inside the smaller of said two other springs and having a length substantially equal to the distance by which the said springs, when fully extended, project out of said tubular member, which lengthA does not exceed that of said tubular member.

References Cited in the file of this patent UNITED STATES PATENTS 259,381 Godley June 13, 1882 1,825,093 Sansburn Sept. 29, 1931 2,241,193 Garnett et al May 6, 1941 2,315,816 Rodgers Apr. 6, 1943 2,355,520 Fischer Aug. 8, 1944 2,396,448 Stevens l Mar. 12, 1946 2,563,370 Reese Aug. 7, 1951 2,756,014 iLeibfried July 24, 1956 2,783,039 Wilson Feb. 26, 1957 FORELGN PATENTS 169,896 Great Bnitain Oct. 13, 1921 

